Seat device having a function of retaining person&#39;s seated position

ABSTRACT

A device for retaining a person&#39; seated position is provided as seats for vehicles, for example. The device has a seat member and an upper body support member. The seat member a seat surface on which a person is seated. The upper body support member has an upper body support surface that supports an upper body back of the person. The upper body support surface has a pair of support projections for ilia, which are fit to a pair of ilium projections of the person, the ilium projections being projected rearward when the person is seated on the seat surface of the seat member. The seat surface has a pair of accommodating recesses for ischiums, which accommodates therein a pair of ischium projected portions of the person, the ischium projected portions being projected downward.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromearlier Japanese Patent Application No. 2010-188418 filed Aug. 25, 2010,the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a seat device having a function ofretaining a person's seated position, and in particular, the seat devicewhich can be realized as seats for vehicles, for example.

2. Related Art

It is known that chairs are widely used as seated position retentiondevices. Such a chair includes a seat member on which a person is seatedand an upper body support member that supports the upper back of theperson. It is also known to use items for covering a chair and placed ona chair. In order to allow a person to be seated with ease, varioussuggestions have been made regarding the shapes of these seated positionretention devices.

For example, a patent document JP-A-H07-315089 discloses a pelvissupport mechanism for vehicle seats. In this mechanism, a seat back(upper body support member) is divided into two members of an upper backand a lower back, and the lower back is made rotatable at a levelcorresponding to a lumbar support position. The angle of the lower backis adjusted so as to be suitable for a hip point of a seated person, sothat a gap will not be formed between a lower portion of the lower backand the seated person's buttocks (e.g., JP-A-H07-315089).

According to the mechanism disclosed in the above patent document, thegap between the lower portion of the lower back and the buttocks isensured to be eliminated to support a portion in the vicinity of thebuttocks. This mechanism will mitigate the load imposed on the lumbarregion, compared to the case where load is concentrated on the lumbarregion. However, this mechanism may cause the buttocks to be shiftedforward to thereby cause a so-called submarining phenomenon in which thepelvis leans rearward. In such a case, a gap is eventually formedbetween the buttocks and the seat back. The mechanism disclosed in thispatent document will not allow the seated person to be easily get tired,by eliminating a gap between the lower portion of the lower back and thebuttocks. This will retain the seated person's adequate posture in anindirect manner but the posture is not retained sufficiently easily.

SUMMARY

Hence it is desired to provide a seated position retention device or aseat device with which a person who is seated on the device is able toeasily retain an adequate posture of a seated person.

In the present disclosure, “retaining a person's seated position”intends to mean “assisting a person to retain their seating position.”

In order to achieve the above object, according to a first aspect of thepresent disclosure, the position retention device or the seat device(hereinafter, the “the seat device” conceptually includes the satedposition retention device) of the present disclosure includes an upperbody support surface provided with a pair of ilium support projections(or simply support projections) which are fitted to a pair of iliumprojections. Thus, for a person in a seated state, a force is applied tothe ilium projections from the respective ilium support projections. Theilium projections are located in an upper part of a pelvis andtherefore, in a state where the ilium projections are supported by theilium support projections, the pelvis is applied with a force in adirection of allowing the pelvis to lean forward. Accordingly, asubmarining phenomenon in which the pelvis leans rearward is unlikely tobe caused.

In a state where the pelvis does not lean rearward, the force applied bythe upper body to the pelvis is large. However, in the presentdisclosure, the seated position retention device has a seat surfaceprovided with ischium accommodating recesses which accommodaterespective ischium projection shaping portions. Thus, in a state wherethe force applied to the ischia by the upper body is large, a posturewhere the ischia are accommodated in the respective ischiumaccommodating recesses is easily retained. For these reasons, asubmarining phenomenon is unlikely to be caused and, in addition, theadequate posture of a seated person is easily retained. Since theadequate posture is easily retained, the seated person will recover fromfatigue earlier.

When a seated person holds the person's feet on the floor, the reactionforce transferring from the soles to the trunk is received by the iliumsupport projections via the ilium projections. The ilium supportprojections are projected out of the area where they are provided.Accordingly, the reaction force mentioned above is mainly received bythe ilium support projections, reducing the rate that the reaction forceis received by portions other than the ilium support projections.

Specifically, the rate of reaction force received by the upper bodysupport surface via backbones and lumbar region becomes small. Thus, theload imposed on the backbones and lumbar region is mitigated. Also, theilium projections do not feel so much pain when a large force is appliedfrom outside. For these reasons, compared to normal chairs that allow anupper body of a seated person to be mainly supported by backbones andlumbar region, the load imposed on the seated person's body is reducedeven when the person fully holds the person's feet on the floor. Thus, aseated person also can hold their feet on the floor. In this way, theseated position retention device of the present disclosure may beparticularly favorably used for a driver's seat of a vehicle in which aseated person is required to operate the brake pedal or the acceleratorpedal.

The size of pelvis depends on individual persons. Accordingly, thepositions of ischia and ilia, which are parts of pelvis, in a seatedstate depend on individual persons. Therefore, it will be most preferredto determine the positions of the ilium support projections and theischium accommodating recesses on an individual person basis.

Meanwhile, the size of pelvis is not so greatly different betweenindividual persons if the individual persons are adults. Therefore, thepositions of the ilium support projections and the ischium accommodatingrecesses may not be required to be determined on an individual personbasis. In this case, the positions of the ilium support projections andthe ischium accommodating recesses may be determined by limitingattributes, such as male adult or female adult, of a seated person andconsidering an average pelvis of the persons having the limitedattributes. More preferably, the size of the ilium support projectionsand the ischium accommodating recesses may be determined considering avariation range of the pelvises of the persons having the attributes.

According to a second aspect of the present disclosure, the upper bodysupport surface includes rib support slant ridges (or simply slantridges) which are fitted to the ribs from beneath descending inexhalation. The rib support slant ridges are slanted along theinclination of the ribs. The ribs are supported by the rib support slantridges and thus the seated person's upper body is suppressed fromhorizontal sway. The provision of the rib support slant ridges alsomakes it easy to retain an adequate posture of a seated person. Inaddition, an advantage of easing the seated person's breathing is alsoobtained. The reasons why the seated person's breathing is eased will bedescribed later.

It is preferred, as in a third aspect of the present disclosure, thatthe rib support slant ridges are provided so as to be positioned betweenthe ninth and the tenth ribs, being in contact with them. Although thedetails will be described later, this will particularly enhance theadvantage of easing seated person's breathing.

It is preferred, as in a fourth aspect of the present disclosure, thatthe seat surface further includes a pair of thigh position referenceridges (or simply reference ridges) each of which is fitted to a recessbetween the biceps femoris muscle and the semimembranosus muscle of therespective one of the left and right thighs.

Being provided with the thigh position reference ridges, the thighs of aperson in a seated state will stably stay in position. When the upperbody of the seated person is moved in the horizontal direction as well,the upper body is easily restored to an original posture with referenceto the thighs and the person can stably stay in position. Thus, theposture of the seated person is more easily retained. Since it isimportant to stably keep a seated person's upper body in position whilethe person is driving a vehicle, the seated position retention device ofthe present disclosure is particularly favorable when used for adriver's seat of a vehicle.

With a normal chair, when the lower legs of a seated person are moved,the thighs are also moved interlocking with the motion of the lowerlegs. However, being provided with the thigh position reference ridges,the thighs are permitted to stably stay in position. Thus, the lowerlegs can be moved using the ends of respective thighs, i.e. the knees,as fulcrums. Accordingly, when the lower legs are moved, the thighs aresuppressed from moving interlocking with the motion of the lower legs,leading to easier motion of the lower legs. Thus, use of the seatedposition retention device of the present disclosure for a driver's seatof a vehicle will make it easy for a seated person to operate theaccelerator pedal or the brake pedal. From this viewpoint as well, theseated position retention device of the present disclosure isparticularly favorable when used for a driver's seat of a vehicle.

It is preferred, as in a fifth aspect of the present disclosure, thatthe upper body support surface further includes shoulder blade aidridges (or simply aid ridges). The shoulder blade aid ridges aresubstantially horizontal, being positioned within a vertical rangecovering the fifth to the seventh ribs. Each of the shoulder blade aidridges has a backbone-side end portion positioned between backbones andthe corresponding shoulder blade.

The shoulder blade aid ridges, being substantially horizontallyprovided, hinder a horizontal tilting motion of a seated person's upperbody. Thus, since the horizontal tilting motion of the seated person'supper body is suppressed, the adequate posture of the person is moreeasily retained.

On the other hand, a rotational motion of the upper body centeringbackbones will not be hindered by the shoulder blade aid ridges.Accordingly, when the seated person looks left or right, the horizontalsway of the upper body is suppressed, while the rotational motion of theupper body for turning the person's face to the left or right isaccelerated. As a result, undesirable horizontal sway of the head duringdriving is suppressed. Accordingly, the seated position retention deviceof the present disclosure is favorable when used for a driver's seat ofa vehicle.

Being provided with the shoulder blade aid ridges, a backbone-side endportion of each of the shoulder blade aid ridges, which is positionedbetween backbones and a backbone-side end of the corresponding shoulderblade, is used as a fulcrum of turn of the person in a seated state,aiding the turning of the corresponding shoulder blade. Thus, the motionof the shoulders accompanying the turning of the shoulder blades is madeeasy. Accordingly, use of the seated position retention device of thepresent disclosure for a driver's seat of a vehicle will allow theseated person to handle the steering wheel with ease.

Shoulder blades are pulled downward by lower trapezius muscles.Meanwhile, shoulder blades are supported by the respective shoulderblade aid ridges. Therefore, the shoulder blades are suppressed frombeing lowered. This will also help realizing easy turning of theshoulders.

In addition to the shoulder blade aid ridges, it is preferred, as in asixth aspect of the present disclosure, that the upper body seat surfacefurther includes lower rib horizontal ridges (or simply horizontalridges) which are substantially horizontal and positioned within a rangecovering the tenth to the twelfth ribs. The lower rib horizontal ridgesalso hinder a seated person's tilting motion of the upper body in thehorizontal direction. Thus, with the horizontal tilting motion of theupper body being suppressed, the adequate posture of the seated personis more easily retained.

It is preferred, as in a seventh aspect of the present disclosure, thatthe ilium support projections are provided in a lower part of the upperbody support surface, which is separated from an upper part includingthe rib support slant ridges. In this case, the lower part including theilium support projections is undetachably connected to the seat surface,while the upper part including the rib support slant ridges is madevertically movable with respect to the seat surface.

A rib position relative to the seat surface varies comparatively greatlydepending on individual persons. Therefore, when the upper part of theupper body support surface including the rib support slant ridges ismade vertically movable, the position of the rib support slant ridgesmay be brought to the position matching the rib position which variesdepending on individual persons.

On the other hand, an ilium position relative to the seat surface is notso different between individual persons. Therefore, if the lower partincluding the ilium support projections is also moved in the verticaldirection together with the upper part including the lower ribhorizontal ridges, the ilium support projections may not be fitted tothe respective ilium projections. In this regard, according to theseventh aspect of the present disclosure, the lower part including theilium support projections is undetachably connected to the seat surface.Thus, when the rib support slant ridges are vertically moved, the lowerpart including the ilium support projections will stay unmoved in thevertical direction. Accordingly, while the rib support slant ridges arevertically moved, the state where the ilium support projections arefitted to the respective ilium projections is retained.

In the case, as well, where the upper body support surface includes theshoulder blade aid ridges in addition to the ilium support projections(fifth aspect), it is preferred, as in an eighth aspect of the presentdisclosure, that an upper part of the upper body support surfaceincluding the shoulder blade aid ridges may be separated from a lowerpart including the ilium support projections. In this case, the lowerpart is undetachably connected to the seat surface, while the upper partis made vertically movable with respect to the seat surface. Thus, theposition of the shoulder blade aid ridges can be changed so as to besuitable for an actual user, while the state where the ilium supportprojections are fitted to the respective ilium projections of the useris retained.

The range in which the upper part of the upper body support surface ismade movable in the eighth aspect is ensured to include a variationrange of a height of the fifth to the seventh rib from the seat surface,which height varies depending on individual persons.

In the case where the upper body support surface is divided into theupper part and the lower part and the upper part includes the ribsupport slant ridges (seventh aspect), it is preferred, as in a ninthaspect of the present disclosure, that the upper part further includesshoulder blade aid ridges. Further, it is preferred, as in a tenthaspect of the present disclosure, that the upper part further includeslower rib horizontal ridges. Thus, the positions of the shoulder bladeaid ridges and the lower rib horizontal ridges are adjusted to thepositions of the shoulder blades and the lower ribs, respectively, whichvary depending on individual persons.

According to an eleventh aspect of the present disclosure, a pair ofslant ridges are provided. These slant ridges are substantially the sameas the rib support slant ridges. Thus, according to the eleventh aspectof the present disclosure, the same advantage as that of the seventhaspect is obtained.

According to a twelfth and a thirteenth aspects of the presentdisclosure, a pair of substantially horizontal ridges are provided.These ridges are substantially the same as the shoulder blade aidridges. Thus, according to the twelfth and the thirteenth aspects of thepresent disclosure, the same advantages as those of the eighth and theninth aspects are obtained.

According to a fourteenth aspect of the present disclosure, a pair ofsubstantially horizontal ridges are provided below the slant ridges.These ridges below the slant ridges are substantially the same as thelower rib horizontal ridges. Thus, according to the fourteenth aspect ofthe present disclosure, the same advantage as that of the tenth aspectis obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

In the accompanying drawings:

FIG. 1 is a perspective view illustrating a seat according to anembodiment of a seat device of the present invention;

FIG. 2 is a schematic front view illustrating a pelvis of an adult male;

FIG. 3 is a vertical cross sectional view illustrating the seat takenalong a plane passing through a pair of ischium accommodating recesses(i.e. taken along a line III-III of FIG. 1);

FIG. 4 is a side view illustrating the pelvis of an adult male;

FIG. 5 is a schematic top view illustrating the pelvis of an adult male;

FIG. 6 is a cross-sectional view illustrating the seat taken along aplane passing through the centers of a left ilium support projection, aleft ischium accommodating recess and a left thigh position referenceridge (i.e. taken along a line VI-VI of FIG. 1);

FIG. 7 is a cross-sectional view taken along a plane passing through apair of ischium accommodating recesses (i.e. taken along a line VII-VIIof FIG. 1);

FIG. 8 is a schematic structural view illustrating ribs, shoulder bladesand backbones; and

FIG. 9 is an illustration conceptually explaining an inseparable portionand a separable and movable structure of a seat according to amodification of the present embodiment and a cover on the seat where thepresent invention can also be applied on the cover.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, hereinafter will bedescribed an embodiment of a seat device for retaining person's seatedposition (conceptually includes the seated position retention device)according to the present invention.

In the embodiment, “retaining a person's seated position” intends tomean “assisting a person to retain their seating position.”

FIG. 1 is a perspective view illustrating a seat 1 according to anembodiment of the seat device with the seated position retentionfunction. The seat 1 is used as a driver's seat of a vehicle.

The seat 1 includes a seat member 10, an upper body support member (orbackrest) 20 and a headrest 30. The seat member 10, the upper bodysupport member 20 and the headrest 30 have surfaces made of the samematerial, i.e. these members are covered with the same soft material,such as fabric or leather. The seat member 10 serves as a member to beseated by a person. The upper body support member 20 serves as a memberfor supporting the upper body, such as the lumbar back or upper bodyback, of the person. The headrest 30 serves as a member for supportingthe back of the head of the person.

In the present embodiment, horizontal, longitudinal and verticaldirections can be set to the seat 1 as illustrated in FIG. 1. Thehorizontal direction is a width direction along which the seat 1 extendslaterally in its front view or its rear view, the longitudinal directionis a depth direction along which the seat 1 extends in one of its sideviews, and the vertical direction is a height direction along which theseat 1 extends from a vehicle floor, for example.

The seat member 10 has an upper surface, i.e. a seat surface 11, inwhich a pair of ischium accommodating recesses 40 and a pair of thighposition reference ridges 70 are formed. FIG. 2 is a schematic frontview illustrating a pelvis 50 of an adult male. As shown in FIG. 2, twoischia 60 in the pelvis have respective two ischium projected portions61. When a person is seated on the seat surface 11, the ischiumaccommodating recesses 40 accommodate the respective ischium projectedportions 61 via the skin and the flesh.

The position of the ischium accommodating recesses 40 in the seatsurface 11 is determined such that the ischium accommodating recesses 40are ensured to be opposed to the respective ischium projected portions61, when a person is seated on the seat surface 11. Thus, the pelvis andthe back of the person will be supported by the upper body supportmember 20. The position of the ischium accommodating recesses 40 in theseat surface 11 is determined based on the size of the pelvis 50 ofaverage adults.

FIG. 3 is a vertical cross-sectional view illustrating the seat member10, taken along a plane passing between the pair of ischiumaccommodating recesses 40 (i.e. taken along line III-III of FIG. 1). Asshown in FIG. 3, the ischium accommodating recesses 40 each have a shapeof a bowl. Specifically, each ischium accommodating recess 40 has acenter at the deepest position thereof toward which the recess 40 isslanted to an extent of a shallow bowl.

As shown in FIG. 3, the ischium accommodating recesses 40 are providedso as to be symmetric with reference to a widthwise center plane C1 ofthe seat member 10. The two ischium accommodating recesses 40 have aspacing therebetween and a widthwise length, which are determined basedon the spacing and the size of the two ischium projected portions 61 ofaverage adults. Also, the degree of slant and the depth as well as alongitudinal length (perpendicular to the widthwise direction), notshown, of each of the ischium accommodating recesses 40 are alsodetermined based on the size of the pair of ischium projected portions61 of average adults.

The spacing and the size of the two ischium projected portions 61 ofaverage adults here may be obtained taking into account both or eitherof adult males and adult females. Whether the adults taken into accountshould include both of males and females or either of males and femalesmay be determined based on the usage of the seat 1. The average adultsthat should be taken into account are determined in the same manner asthe above, in determining the position of the ischium accommodatingrecesses 40 in the seat surface 11. Also, depending on the usage, theposition of the ischium accommodating recesses 40 may be determinedbased on the spacing and the size of a pair of ischium projectedportions of children. Further, the position of the ischium accommodatingrecesses 40 may be determined based on the spacing and the size of apair of ischium projected portions of an individual person.

Referring again to FIG. 1, the configuration of the seat surface 11 isfurther described. In the seat surface 11, the pair of thigh positionreference ridges 70 are formed. Also, the seat surface 11 has sideslocated in the widthwise direction, both of which are slightly uplifted.

Each thigh has, on its back, a biceps femoris muscle and asemimembranosus muscle. There is a recess between these biceps femorismuscle and semimembranosus muscle. In other words, there is a portionbetween these biceps femoris muscle and semimembranosus muscle, whichportion more easily sinks when pushed from immediately above thesemuscles than when pushed from outside. This recess resides inapproximately the center in the widthwise direction of the back of athigh. Since both of the biceps femoris muscle and the semimembranosusmuscle extend in the longitudinal direction of the thigh, the recesstherebetween also extends in the longitudinal direction.

The pair of the thigh position reference ridges 70 are each provided soas to be fitted to the recess between the biceps femoris muscle and thesemimembranosus muscle. For this reason, specifically, the pair of thighposition reference ridges 70 are extended from near the position wherethe pair of ischium accommodating recesses 40 are formed toward aknee-side end portion 12 of the seat member 10. In this case, the twothigh position reference ridges 70 are made parallel to each other, or,alternatively, may be slightly distanced from each other as the ridges70 near the knee-side end portion 12.

Further, the height, the longitudinal length and the widthwise length ofeach of the two thigh position reference ridges 70 as well as thespacing therebetween are determined such that each of the ridges 70 iseasily fitted to the recess between the biceps femoris muscle and thesemimembranosus muscle when a person is seated on the seat surface 11.The thigh position reference ridges 70 are each formed by placing amaterial beneath the material configuring the surface of the seat 1. Thematerial placed beneath the material configuring the surface of the seat1 has a rigidity that can maintain the shape of each of the thighposition reference ridges 70 when thighs are located on the respectiveridges 70.

Hereinafter, the configuration of the upper body support member 20 isdescribed. As shown in FIG. 1, the upper body support member 20 has anupper body support surface 21 in which a pair of ilium supportprojections 80 are formed at a lower portion thereof. The two iliumsupport projections 80 are formed at the same level from the seatsurface 11 and have the same size and the same degree of projection.

FIG. 4 is a side view illustrating the pelvis 50, which is taken along aVI-VI line in FIG. 1. As shown in FIG. 4, ilia 90 configuring the upperportion of the pelvis 50 have respective projections 91 which areprojected rearward (hereinafter referred to as “ilium projections 91”).FIG. 5 is a schematic top view illustrating the pelvis 50 of a maleadult. As shown in FIG. 5, the ilium projections 91 are located on bothsides of backbones 92, or located sandwiching the backbones 92. In eachilium projection 91 having a projected shape, the vertical length issmall but, compared to this, the horizontal length is large. The iliumsupport projections 80 provided in the upper body support member 20 areconfigured to be fitted to the respective ilium projections 91 via theskin and the flesh of a seated person. The position of the ilium supportprojections 80 is determined based on the size of the pelvis of averageadults. The average adults to be taken into account are determined inthe same manner as mentioned above.

FIG. 6 is a cross-sectional view of the seat 1 taken along a planepassing through the centers of the left ilium support projection 80, theleft ischium accommodating recess 40 and the left thigh positionreference ridge 70 (i.e. taken along a line VI-VI of FIG. 1). FIG. 7 isa cross sectional view taken along a plane passing through the pair ofilium support projections 80 (i.e. taken along a line VII-VII of FIG.1). As will be understood from FIGS. 6 and 7, the shape of each iliumsupport projection 80 is not a projection slanted upward, downward andleftward and rightward centering on the peak point. Instead, the iliumsupport projection 80 has the most projected portion which isapproximately linearly shaped, matching the shape of the correspondingilium projection 91. Also, as will be understood from FIG. 7, each iliumsupport projection 80 is linearly slanted toward the widthwise center ofthe upper body support surface 21. In other words, the degree ofprojection of each ilium support projection 80 becomes smaller towardthe widthwise center of the upper support surface 21. Such a slant ofeach ilium support projection 80 also helps the projection 80 moresuitably fitted to each of the corresponding ilium projections 91.

The position of the two ilium support projections 80 relative to theseat surface 11 and the spacing between the two ilium supportprojections 80 are determined based on the spacing and the size of thepair of ilium projections 91 of average adults. The size of each iliumsupport projection 80 is determined ensuring to support thecorresponding ilium projection 91 but ensuring not to support otherportions of the upper body as much as possible. It should be appreciatedthat the average adults that should be taken into account in determiningthe position and the spacing of the ilium support projections 80 aredetermined in the same manner as in the case of the ischiumaccommodating recesses 40.

The ilium support projections 80 are each formed by placing a materialbeneath the material configuring the surface of the seat 1. The materialplaced beneath the material configuring the surface of the seat 1 has arigidity that can maintain the shape of each of the ilium supportprojections 80 when the respective ilium projections 91 are supported bythe ilium support projections 80. When the brake pedal or theaccelerator pedal is fully stepped on, the depression force is large andthus the reaction force is also large. As a result, a large force may beimposed on the ilium support projections 80. For this reason, it ispreferred that the ilium support projections 80 have a rigidity which isable to maintain the shape of themselves when such a large reactionforce is imposed.

The upper body support surface 21 of the upper body support member 20 isfurther provided with a pair of rib support slant ridges 100 and a pairof shoulder blade aid ridges 110 and a pair of lower rib horizontalridges 120.

The rib support slant ridges 100 are ensured to fit to ribs from beneathwhen the ribs descend with exhalation. The “ribs that descend withexhalation” mainly refer, here, to the ninth to the twelfth ribs towhich respective inferior posterior serratus muscles are connected.Accordingly, the rib support slant ridges 100 are each located at aposition that allows the ridge 100 to fit to any one of the ninth totwelfth ribs from beneath. For example, the rib support slant ridges100, when being fitted to the respective ninth ribs from beneath, areeach positioned between the ninth and the tenth ribs, being in contactwith them.

The ninth to the twelfth ribs are connected to the ribs located athigher positions through body tissues, and thus the ribs located higherthan the ninth ribs also descend with exhalation. Accordingly, forexample, the rib support slant ridges 100 may be positioned between theeighth and the ninth ribs, being in contact with them.

As shown in FIG. 1, the two rib support slant ridges 100 of the presentembodiment are spaced apart from each other. The length of the spacingis made larger than the thickness of the backbones so that the backbonesare prevented from being pressed by the rib support slant ridges 100.Also, each one of the rib support slant ridges 100 is slanted downwardfrom an end portion thereof near the other one of the rib support slantridges 100 (backbone-side end portion) toward the other end portionthereof (outer end portion). The angle of this slant is ensured tosubstantially coincide with the inclination angle of the ribs againstwhich the rib support slant ridges 100 are fitted.

The rib support slant ridges 100 each have the length, thickness andrigidity as described below. Specifically, the length may preferably beset to an average length of the ribs (e.g., the ninth ribs) to be fittedto. However, the length larger or smaller than this may also allow therib support slant ridges 100 to exert the effects thereof. The thicknessis ensured to be smaller than the distance between the pair of ribs tobe fitted to and the pair of ribs located immediately beneath the pairof ribs to be fitted to, but to be large enough to support the pair ofribs to be fitted to. For example, the thickness may be approximatelythe same as the thickness of the pair of ribs to be fitted to. Therigidity is set to a level that will not allow a seated person to behurt when the person leans back to the upper body support member 20, butwill allow the rib support slant ridges 100 to adequately support theribs.

In a person's seated state, the position of the person's ribs relativeto the seat surface 11 may comparatively greatly differ, depending onthe persons seated. For this reason, the position of the person's ribsrelative to the seat surface 11 is determined based on an average bodysize. Nevertheless, depending on the persons seated, the position of therib support slant ridges 100 may not match the position of the person'sninth ribs to be fitted to from beneath.

However, as mentioned above, the rib support slant ridges 100 do nothave to be necessarily fitted to the ninth ribs but may be fitted to thetenth or the eleventh ribs, or alternatively, may be fitted to theeighth ribs. In addition, the inclination angles of these ribs do nogreatly differ from each other. Accordingly, although the position ofthe rib support slant ridges 100 relative to the seat surface 11 isfixed in the present embodiment, a person of any seating height may beseated on the seat 1 to have the rib support slant ridges 100 fitted tothe person's descending ribs from beneath in exhalation.

The pair of shoulder blade aid ridges 110 are positioned within avertical range covering the fifth to the seventh ribs of a seatedperson. Accordingly, as shown in FIG. 1, the shoulder blade aid ridges110 are located above the rib support slant ridges 100. The two shoulderblade aid ridges 110, each being substantially horizontal, arejuxtaposed in the horizontal direction. The “substantially horizontal”here refers to that these ridges 110 are slanted to an extent of theinclination angles of the fifth to the seventh ribs in the state wherethe backbones of the seated person are upright.

Referring to FIG. 8, the shoulder blade aid ridges 110 are specificallydescribed. FIG. 8 is a schematic structural view illustrating ribs,shoulder blades and backbones.

Each of the shoulder blade aid ridges 110 has a backbone-side endportion which is ensured to be positioned between a backbone-side end ofthe corresponding shoulder blade and the backbones. The length from awidthwise center line C2 (see FIG. 1) of the upper body support surface21 to the backbone-side end portion of each shoulder blade aid ridge 110is figured out as follows. Specifically, this length is equal to orlarger than a horizontal length d1 from a backbone center line C2′ to abackbone end, which corresponds to half the thickness of each backbone(see FIG. 8), but equal to or smaller than a horizontal length d2 fromthe backbone center line C2′ to an outer end of a part of thecorresponding shoulder blade, which falls within the range of from thefifth to the seventh ribs (see FIG. 8).

However, since shoulder blades are capable of various motions, thelength d2 changes with the motion of each of the shoulder blades.Therefore, the length d2 that should be taken into account is renderedto be the minimum length d2 in the turning motion of the shoulderblades.

As mentioned above, in a person's seated state, the rib position of theperson relative to the seat surface 11 may comparatively greatly differ,depending on the persons seated. For this reason, the rib position ofthe person relative to the seat surface 11 is determined based on anaverage body size. Also, the longitudinal length of each of the shoulderblade aid ridges 110 is not particularly limited if only the shoulderblade aid ridges 110 can be formed in the upper body support surface 21.For example, each of the shoulder blade aid ridges 110 may have alongitudinal length corresponding to approximately half the widthwiselength of the back of a person of an average size.

The vertical position of the pair of lower rib horizontal ridges 120 isdetermined taking into account a seating height of average persons.Specifically, the lower rib horizontal ridges 120 are formed within avertical range covering the tenth to the twelfth ribs which are locatedat the lowest in all of the ribs. Accordingly, as shown in FIG. 1, thelower rib horizontal ridges 120 are positioned below the rib supportslant ridges 100 and above the ilium support projections 80.

The two lower rib horizontal ridges 120, each being substantiallyhorizontal, are juxtaposed in the horizontal direction. The“substantially horizontal” here refers to that these ridges 120 areslanted to an extent of the inclination angles of the tenth to thetwelfth ribs in the state where the backbones of the seated person areupright. The horizontal position and the length of the pair of lower ribhorizontal ridges 120 are not particularly limited. However, it ispreferable that the lower rib horizontal ridges 120 are provided so asnot to be in contact with the backbones. To this end, the lower ribhorizontal ridges 120 of the present embodiment each have abackbone-side end portion which is ensured to be distanced from thewidthwise center line C2 of the upper body support surface 21 by thelength d1 (see FIG. 8) or more.

In the present embodiment, each of the rib support slant ridges 100,each of the shoulder blade aid ridges 110 and each of the lower ribhorizontal ridges 120 have respective lengths and positions, which aredetermined so that these ridges, 100, 110 and 120 each have the samelengths L1 and L2 from the widthwise center line C2 to the backbone-sideend portion and to the outer end portion, as shown in FIG. 7.

In the upper body support surface 21 of the present embodiment, theportions F out of the outer end portions of the ridges 100, 110 and 120are curved so as to be projected forward, as shown in FIG. 7. Thus, theupper body of a seated person is unlikely to be imbalanced in thehorizontal direction.

Hereinafter will be described the advantages obtained from the seat 1configured as described above with a person being seated. First, anadvantage of facilitating retention of a seated person's posture isdescribed.

The structure most related to this advantage is the pair of iliumsupport projections 80 and the pair of ischium accommodating recesses40. The pair of ilium support projections 80 formed in the seat 1support the pair of ilium projections 91 of a seated person. In otherwords, it is ensured that a force is applied to the pair of iliumprojections 91 of a seated person from the pair of ilium supportprojections 80. Since the ilium projections 91 are located in an upperpart of the pelvis, the application of a force to the ilium projections91 means that the force is applied to the pelvis such that the person isallowed to lean forward. Thus, a submarining phenomenon in which aseated person's pelvis leans rearward is unlikely to be caused.

In a state where a seated person's pelvis does not lean rearward, theperson's pair of ischium projected portions 61 are accommodated in thepair of ischium accommodating recesses 40 formed in the seat surface 11.Also, in a state where a seated person's pelvis does not lean rearward,the upper body is approximately upright, allowing the upper body to pushthe ischia with a large force. Therefore, a state where the ischia areaccommodated in the respective ischium accommodating recesses 40 can beeasily retained. For these reasons, a submarining phenomenon is unlikelyto be caused and the seated person's upright posture is easily retained.In addition, since the seated person's upright posture is easilyretained, the person will recover from fatigue quickly.

Further, when a seated person holds the person's feet on the floor aswell, the reaction force transferring from the soles to the trunk isreceived by the ilium support projections 80 of the seat 1 via theperson's ilium projections 91. The ilium support projections 80 areprojected out of the area where they are provided. Accordingly, thereaction force mentioned above is mainly received by the ilium supportprojections 80, reducing the rate that the reaction force is received byportions other than the ilium support projections 80.

Specifically, the rate of reaction force received by the upper bodysupport surface 21 via backbones and lumbar becomes small. Thus, theload that will be imposed on the backbones and lumbar is mitigated.Also, human's ilium projections 91 do not feel so much pain when a largeforce is applied from outside. For these reasons, compared to normalchairs that allow an upper body to be mainly supported by backbones andlumbar, the load imposed on a seated person's body is reduced even whenthe person fully holds the person's feet on the floor. Thus, a seatedperson also can fully step on an accelerator pedal or a brake pedal.

Thus, with the seat 1 of the present embodiment, a seated person'sposture is easily retained by the ischium accommodating recesses 40 andthe ilium support projections 80. In addition to this, with the seat 1of the present embodiment, the horizontal motion of the person's upperbody is suppressed by the rib support slant ridges 100, the shoulderblade aid ridges 110 and the lower rib horizontal ridges 120 provided inthe upper body support surface 21. Thus, these ridges 110, 110 and 120also contribute to easy retention of the posture of the seated person.Further, the thigh position reference ridges 70 provided in the seatsurface 11 determine the positions of the thighs. This will also helpeasily retaining the posture of the seated person.

Hereinafter is described an advantage of easing seated person'sbreathing. The structure most related to this advantage is the ribsupport slant ridges 100.

There are various body tissues between ribs, which establish connectionbetween ribs. Accordingly, if the rib support slant ridges 100 are notprovided, muscles (e.g. inferior posterior serratus muscle) thatcontract in exhalation not only allow the ribs, to which the muscles areconnected, to descend, but also allow upper ribs, to which the musclesare not connected, to descend.

In this regard, the seat 1 of the present embodiment is provided withthe rib support slant ridges 100. These rib support slant ridges 100 arefitted to seated person's ribs from beneath, which descend inexhalation. Thus, upper ribs located around the chest are suppressedfrom descending, so that the chest is likely to be kept open.Accordingly, the seated person can breathe with ease.

In particular, the rib support slant ridges 100, when positioned betweenthe ninth and the tenth ribs, will exert a large effect of easing theseated person's breathing. The reason for this is as follows.Specifically, the tenth and lower ribs are included in an abdominalmuscle system to which the abdominal muscles are connected, and thusdescend with the contraction of the abdominal muscles.

On the other hand, the ninth and upper ribs are not connected to theabdominal muscles but to inspiratory muscles. Therefore, when the ribsupport slant ridges 100 are positioned between the ninth and the tenthribs, these ribs are efficiently suppressed from being lowered by themuscles in the abdominal muscle system, while the motion of theinspiratory muscles is not hindered. In this way, the advantage ofeasing the person's breathing is enhanced.

As described above, owing to the configuration such as of the iliumsupport projections 80 and the pair of ischium accommodating recesses40, a seated person's posture is easily retained. In the postureretained such as by the ilium support projections 80 and the pair ofischium accommodating recesses 40, the person will receive less pressureon the chest. Accordingly, the configuration such as of the iliumsupport projections 80 and the pair of ischium accommodating recesses 40also enhances the advantage of easing the person's breathing.

Hereinafter is described an advantage that a seated person's posture iseasily restored to the original posture. The structure most related tothis advantage is the thigh position reference ridges 70.

The thigh position reference ridges 70 are each provided so as to fitinto a recess between the seated person's biceps femoris muscle and thesemimembranosus muscle. When each thigh position reference ridge 70 isfitted to the recess between the biceps femoris muscle and thesemimembranosus muscle, the position of the corresponding thigh isdetermined. With a normal chair, horizontal sway of a seated person'supper body usually allows the thighs to also move interlocking with thehorizontal sway. However, in the present embodiment, the thigh positionreference ridges 70 determine the positions of the respective thighs andthe thighs stably stay at the positions.

Accordingly, when the upper body is imbalanced in the horizontaldirection as well, the thighs are suppressed from moving in thehorizontal direction interlocking with the horizontal imbalance of theupper body. Thus, the positions of the respective thighs serve asreferences. Accordingly, when the upper body is horizontally imbalanced,the upper body can be easily restored to the adequate original posturewith reference to the stably positioned thighs. The adequately posturedupper body will help reduce muscle fatigue of the seated person, and theperson is unlikely to get tired. In addition, in order to drive a carsafely, it is important to stably keep the upper body in position, andthus the seat 1 of the present embodiment is useful for safe driving.

Hereinafter is described an advantage that lower legs are allowed to beeasily moved. The structure most related to this advantage is again thethigh position reference ridges 70.

With a normal chair, when lower legs are moved, the thighs are alsomoved interlocking with the motion of the lower legs. However, in thepresent embodiment, the thigh position reference ridges 70 determine thepositions of the respective thighs and the thighs will stably stay inposition.

Thus, when the lower legs are moved, the knees at the ends of therespective thighs serve as fulcrums. Specifically, when the lower legsare moved, the thighs are suppressed from moving interlocking with themotion of the lower legs, while only the lower legs are allowed to move.Thus, the lower legs are easily moved. Accordingly, the acceleratorpedal or the brake pedal is easily operated. With the easy operation ofthe pedals, fatigue caused during driving is mitigated. It should beappreciated that the advantage of easily retaining a seated person'sposture will also help mitigating fatigue caused during driving.

Hereinafter is described an advantage that horizontal imbalance of aseated person's posture is suppressed. The structures most related tothis advantage are the shoulder blade aid ridges 110 and the lower ribhorizontal ridges 120.

The shoulder blade aid ridges 110, being substantially horizontal,substantially hinder the tilting motion of a seated person's upper bodyin the horizontal direction. As a result, horizontal imbalance of theupper body is suppressed.

On the other hand, a rotational motion of the upper body centering thebackbones will not be hindered by the shoulder blade aid ridges 110.Accordingly, when the seated person looks left or right, the horizontalsway of the upper body is suppressed, while the rotational motion of theupper body for turning the person's face to the left or right isaccelerated. As a result, undesirable horizontal sway of the head duringdriving is suppressed.

The lower rib horizontal ridges 120 are substantially horizontal withina range covering the tenth to the twelfth ribs which are connected tothe abdominal muscles. Thus, the motion of a seated person's abdominalmuscles, which is guided by the lower rib horizontal ridges 120, becomeseasier. This motion corresponds to the rotation of the lumbar. Therotation of the lumbar in other words is the rotational motion of theupper body centering the backbones. Therefore, resultantly, thehorizontal sway of the upper body is also suppressed by the lower ribhorizontal ridges 120. In order that the above advantage is obtained bythe lower rib horizontal ridges 120, it is most favorable that the lowerrib horizontal ridges 120 are brought into contact with the lower endsof the pair of tenth ribs.

Hereinafter is described an advantage that seated person's shoulders arerotated with ease. The structure most related to this advantage is againthe shoulder blade aid ridges 110. When a person is seated on the seat1, a backbone-side end portion of each of the shoulder blade aid ridges110 is positioned between the backbones and a backbone-side end portionof the corresponding shoulder blade. Therefore, the backbone-side endportion of the shoulder blade aid ridge 110 is used as a fulcrum ofturn, and thus the turning of the corresponding shoulder blade is aided.Thus, the motion of the shoulders accompanying turning of the shoulderblades becomes easier. In this way, when the person is seated on adriver's seat, handling of the steering wheel becomes easier.

Shoulder blades are pulled downward by lower trapezius muscles.Meanwhile, shoulder blades are supported by the respective shoulderblade aid ridges 110. Therefore, the shoulder blades are suppressed frombeing lowered. This will also help realizing easy turning of theshoulders.

The present invention is not limited to the embodiment described so far.The following modifications may also fall within the technical range ofthe present invention. Further, the present invention may also bemodified and implemented in various other ways within a range notdeparting from the spirit of the invention.

For example, although only a pair of rib support slant ridges 100 havebeen provided in the above embodiment, two or more pairs may beprovided. For example, a first pair of rib support slant ridges may beprovided between the ninth and the tenth ribs being in contact withthem, and a second pair of rib support slant ridges may be providedbetween the tenth and the eleventh ribs being in contact with them.Thus, the ribs are further suppressed from being lowered, whereby aseated person's breathing is more eased.

In the embodiment described above, the rib support slant ridges 100, theshoulder blade aid ridges 110 and the lower rib horizontal ridges 120have been fixed to the upper support surface 21 (i.e, the seat member 10in the embodiment), or in other words, the positions of these ridgeshave been unchangeable in the vertical direction. However, positions ofthe objects to be supported, i.e. a rib position and a shoulder bladeposition, relative to the seat surface 11 are different comparativelygreatly depending on the persons seated. On the other hand, position ofthe ilium projections 91 relative to the seat surface 11 iscomparatively less different between persons seated. The iliumprojections 91 are supported by the respective ilium support projections80 which are also formed in the upper body support surface 21.

Considering this, the seat 1 may be configured as follows. Specifically,as pictorially shown in FIG. 9, the upper body support member 20 may beseparated into a part that includes the ilium support projections 80(hereinafter referred to as “lower upper-body support LP”) and a partthat includes at least one of the rib support slant ridges 100, theshoulder blade aid ridges 110 and the lower rib horizontal ridges 120(hereinafter referred to as “upper upper-body support UP”). The lowerupper-body support LP may be undetachably connected to the seat surface11 (i.e., the seat member 10 in the embodiment) and the upper upper-bodysupport UP may be made vertically movable with respect to the seatsurface 11. In this case, the upper upper-body support UP is ensured tohave a movable range including a variation range of the positions of theobject ribs for the ridges 100, 110 and 120, relative to the seatsurface 11, which may vary depending on persons seated.

A specific configuration is given here for the vertical movement of theupper upper-body support UP relative to the seat surface 11. Forexample, as conceptually shown in an enlarged part A of FIG. 9, aplurality of metal poles PL may be used for connecting the upperupper-body support UP and the lower upper-body support LP, in a similarmanner to the connection between the upper body support 20 and theheadrest 30.

In the upper body support surface 21, the part included in the upperupper-body support UP corresponds to the “upper part of the upper bodysupport surface”, while the part included in the lower upper-bodysupport LP corresponds to the “lower part of the upper body supportsurface”.

The above embodiment has been described taking as an example the seat 1.However, the present embodiment may be applied to chairs having legs.Such chairs having legs are usually used in a house and a variety ofsuch chairs are available, with the materials of the seat surfaces andupper body support surfaces being wood, vinyl and the like. When thepresent invention is applied to such chairs as well, there is noparticular limitation in the materials of the seat surfaces and theupper body support surfaces, and thus various materials similar to thoseof the chairs of conventional art may be used.

The present invention may be applied to covers CV for chairs and seats(refer to FIG. 9). The covers CV correspond to the seated positionretention device to which the present invention can also be applied.When the present invention is applied to the covers CV as well, theupper upper-body support UP and the lower upper-body support LP may beseparately provided. In this case, the lower upper-body support LP maybe undetachably connected to the seat member and the upper upper-bodysupport UP may be made vertically movable with respect to the seatmember.

When the present invention is applied to the covers CV, a cover for theupper body support surface may not be provided but only a cover for theseat surface may be provided. Alternatively, a cover for the seatsurface may not be provided but only a cover for the upper body supportsurface may be provided.

Though already stated in the foregoing, the three-dimensional sizes andpositions (including slant angles) of the thigh position referenceridges 70, the ilium support projections 80, the lower rib horizontalridges 120, the support slant ridges 100 and the shoulder blade aidridges 110 can be provided as order-made products or ready-made productson the seat device or the cover. In the order-made product, the bodysizes of each person who use the product are reflected in the sizes andpositions of those ridges. In contrast, in the read-made products, thestatistically acquired standard body sizes or statistically acquired,but categorized into a plurality of typical sizes (large, medium orsmall, for example) of persons are reflected in the sizes and positionsof the ridges. In this respect, the sizes and positions of the ridgescan be determined uniquely as a matter of fact.

What is claimed is:
 1. A seat device for retaining a person' seatedposition, comprising: a seat member having a seat surface on which aperson is seated; and an upper body support member having an upper bodysupport surface that supports an upper body back of the person, whereinthe upper body support surface has a pair of support projections forilia, which are fit to a pair of ilium projections of the person, theilium projections being projected rearward when the person is seated onthe seat surface of the seat member, and the seat surface has a pair ofaccommodating recesses for ischiums, which accommodates therein a pairof ischium projected portions of the person, the ischium projectedportions being projected downward.
 2. The seat device of claim 1,wherein the upper body support surface has slant ridges for ribs, theslant ridges touching the ribs of the person from beneath and beingslanted according to the ribs, the ribs descending with person'sexhalation.
 3. The seat device of claim 2, wherein the slant ridges areformed to touch a person's upper body back between a ninth rib and atenth rib of the ribs.
 4. The seat device of claim 1, wherein the seatsurface has a pair of reference ridges each of which is fit to a recessbetween a biceps femoris muscle and a semimembranosus muscle of each ofthighs of the person.
 5. The seat device of claim 1, wherein the whereinthe upper body support surface has aid ridges for shoulder blades, theaid ridges i) being located to be fit to a range of fifth to seventhribs of the ribs in a vertical direction of the seat member, ii) beingsubstantially horizontal to the seat surface, and iii) being locatedsuch that a length from a center line of the upper body support surfacein a width direction thereof to a center-line-side end of each of theaid ridges is equal to or larger than a length from a backbone centerline to a backbone end of the person and equal to or smaller than alength from the backbone center line to a shoulder blade of the person.6. The seat device of claim 5, wherein the upper body support surfacehas horizontal ridges for lower ribs, the horizontal ridges i) beinglocated to be fit to a range of tenth to twelfth ribs of the ribs in thevertical direction and ii) being substantially horizontal to the seatsurface.
 7. The seat device of claim 2, wherein the upper body supportmembers comprises upper and lower support members so as to providemutually separated upper and lower support surfaces respectively, thelower support members being fixed to the seat member and having thelower support surface on which the support projections are formed, theupper support member being movable in a vertical direction of the deviceand having the upper support surface on which the slant ridges areformed.
 8. The seat device of claim 5, wherein the upper body supportmembers comprises upper and lower support members so as to providemutually separated upper and lower support surfaces respectively, thelower support members being fixed to the seat member and having thelower support surface on which the support projections are formed, theupper support member being movable in a vertical direction of the deviceand having the upper support surface on which the aid ridges are formed.9. The seat device of claim 7, wherein the upper support member has aidridges for shoulder blades, the aid ridges i) being located to be fit toa range of fifth to seventh ribs of the ribs in a vertical direction ofthe seat member, ii) being substantially horizontal to the seat surface,and iii) being located such that a length from a center line of theupper body support surface in a width direction thereof to acenter-line-side end of each of the aid ridges is equal to or largerthan a length from a backbone center line to a backbone end of theperson and equal to or smaller a length from than the backbone centerline to a shoulder blade of the person.
 10. The seat device of claim 9,wherein the upper support surface has horizontal ridges for lower ribs,the horizontal ridges i) being located to be fit to a range of tenth totwelfth ribs of the ribs in the vertical direction and ii) beingsubstantially horizontal to the seat surface.
 11. The seat device ofclaim 1, wherein the upper body support surface has a pair of slantridges which are slanted at an angle substantially equal to aninclination angle of the ninth or tenth rib of the person, the slantridges being located on both sides of a center line of the upper bodysupport surface in a width direction thereof and being slanted asadvancing from the center line, and the upper body support memberscomprises upper and lower support members so as to provide mutuallyseparated upper and lower support surfaces respectively, the lowersupport members being fixed to the seat member and having the lowersupport surface on which the support projections are formed, the uppersupport member being movable in a vertical direction of the device andhaving the upper support surface on which the pair of slant ridges areformed.
 12. The seat device of claim 1, wherein the upper body supportsurface has a pair of substantially horizontal ridges which are locatedon both sides of a center line of the upper body support surface in awidth direction of the device, and the upper body support memberscomprises upper and lower support members so as to provide mutuallyseparated upper and lower support surfaces respectively, the lowersupport members being fixed to the seat member and having the lowersupport surface on which the support projections are formed, the uppersupport member being movable in a vertical direction of the device andhaving the upper support surface on which the pair of substantiallyhorizontal ridges are formed.
 13. The seat device of claim 11, whereinthe upper support surface has a pair of substantially horizontal ridgeswhich are located on both sides of a center line of the upper bodysupport surface in the width direction, the pair of substantiallyhorizontal ridges being located over the pair of slant ridges in thevertical direction.
 14. The seat device of claim 13, wherein the uppersupport surface has a pair of substantially horizontal ridges which arelocated on both sides of a center line of the upper body support surfacein the width direction, the pair of substantially horizontal ridgesbeing located under in the vertical direction.
 15. A device forretaining a person' seated position, comprising: a seat surface on whicha person is seated; and an upper body support surface that supports anupper body back of the person, wherein the upper body support surfacehas a pair of support projections for ilia, which are fit to a pair ofilium projections of the person, the ilium projections being projectedrearward when the person is seated, and the seat surface has a pair ofaccommodating recesses for ischiums, which accommodates therein a pairof ischium projected portions of the person, the ischium projectedportions being projected downward.
 16. The device of claim 15, whereinthe upper body support surface has slant ridges for ribs, the slantridges touching the ribs of the person from beneath and being slantedaccording to the ribs, the ribs descending with person's exhalation. 17.The device of claim 16, wherein the slant ridges are formed to touch aperson's upper body back between a ninth rib and a tenth rib of theribs.
 18. The device of claim 15, wherein the seat surface has a pair ofreference ridges each of which is fit to a recess between a bicepsfemoris muscle and a semimembranosus muscle of each of thighs of theperson.
 19. The device of claim 15, wherein the wherein the upper bodysupport surface has aid ridges for shoulder blades, the aid ridges i)being located to be fit to a range of fifth to seventh ribs of the ribsin a vertical direction of the seat surface, ii) being substantiallyhorizontal to the seat surface, and iii) being located such that alength from a center line of the upper body support surface in a widthdirection thereof to a center-line-side end of each of the aid ridges isequal to or larger than a length from a backbone center line to abackbone end of the person and equal to or smaller than a length fromthe backbone center line to a shoulder blade of the person.
 20. Thedevice of claim 19, wherein the upper body support surface hashorizontal ridges for lower ribs, the horizontal ridges i) being locatedto be fit to a range of tenth to twelfth ribs of the ribs in thevertical direction and ii) being substantially horizontal to the seatsurface.